Hydraulic safety override valve

ABSTRACT

A hydraulic control valve for controlling a vehicle transmission comprising a manually actuable position selector valve for alternatively directing hydraulic fluid to first or second position clutches of the transmission from a neutral position, a pressure modulating relief valve for modulating the operation of the position selector valve, and a safety override valve linked to the position selector valve for automatically returning the position selector valve to the neutral position when hydraulic pressure is low thereby avoiding system damage.

9 i 1x Mute States 1 atom assume arms Feb. 8, 1972 [54] HYDRAULIC SAFETYOVERRHDE 2,527,727 10/1950 Hobbs ....92/13l X VALVE 2,753,024 7/1956Weaving et a]. ....74/364 X 3,106,135 10/1963 McAfee, Jr. et a1.....92/l3l X [721 Barnes Pwmi 3,243,025 3/1966 Staab et al. ..192/s7.19[73] Assignee: Caterpillar Tractor (30., Peon'a, 111.

. Primary ExaminerCarlton R. Croyle [22] filed May 1970 AssistantExaminerThomas C. Perry [21] App]. No: 411,202 AtzorneyFryer, Tjensvold,Feix, Phillips & Lempio 52 us. Cl ..74/364, 74/753, 91/360, {57]ABSTRACT 92/131, 137/624-27, 192/3719 A hydraulic control valve forcontrolling a vehicle transmisl l f Fl5b 5 /00 sion comprising amanually actuable position selector valve [58] Field of Search..192/87.19, 133;91/360; f alternatively directing hydraulic fl id to fit or Second 92/131, 75; 137/62427; 74/753 364 position clutches of thetransmission from a neutral position, a pressure modulating relief valvefor modulating the operation [56] References of the position selectorvalve, and a safety override valve UNITED STATES PATENTS linked to theposition selector valve for automatically returning the positionselector valve to the neutral position when $352,394 11967 Longshol'ehydraulicpressureislowtherebyavoidingsystemdamage. 2,488,540 11/1949Hollingsworth ..74/364X 2,491,087 12/1949 Cardwellet a1 ..74/3649Claims,lDrawingFigure I '34 A L /I ieo 142 I44 r R ififi A p it /45i-;&:=l3 2; 140214 /'-42 z .6 V 150 126/ Z I29 V v 1, 22 1211 H 54 Q t T @a|I 6 i0 52 \f //4 a 62 l 591 581.1: HI :2:

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INVENTOR [4 v RANDOLPH C. BARNES BY g-Mmu W637 ATTORNEYS HYDRAULICSAFETY OVElRRHDE VALVE BACKGROUND OF THE INVENTION This invention isdirected to a hydraulic control valve or means having control linkagefor effecting shifting of a vehicle transmission of the two-positiontype in which shifting is accomplished by hydraulic pressure applied tocontrol clutches in the transmission unit. The control valve includes asafety override valve which returns the control linkage of thecontrolvalve to a neutral position when hydraulic pressure is low, such asduring hydraulic valve malfunction or normal shutdown of the hydraulicpressure power source which supplies the system hydraulic pressure.

This invention is applicable for use with a transmission of thetwoposition type such as a forward-reverse or a high-low unit. With theforward-reverse unit, the first position of the transmission correspondsto a forward gear while the second position corresponds to a reversegear. Similarly, with the high-low transmission or gear reduction unit,the first position corresponds to a high-speed gear while the secondcorresponds to a low-speed gear. In the following discussion, thehigh-low gear reduction unit is discussed. This is not to be taken aslimiting the scope of the invention narrowly to a highlow transmission.Rather, the invention is broadly directed to a control valve for usewith a two position transmission. Therefore, the following discussion ofthe invention in association with a high-low gear reduction unit is byway of example only.

This invention is particularly directed to application on agriculturaltrack-type tractors. Such tractors have the in herent problem of havingto negotiate difficult terrain in their normal working environment. Inso doing, it is a common practice for operators to shift down into alower speed range for a short period of time in order to transfer moretorque to the vehicle drive line.

High-low ratio gear reduction units have proved to be advantageous inthis application. Such units allow shifting down into the low speedrange by hydraulic means. In order to effect such down -shifting,control means must be provided to enable direction of hydraulic flllltlunder pressure to actuation means such as clutches, therebyalternatively engaging either high or low speed ranges. The use ol'sucha high-low gear reduction unit enables the utilization ofastraight-shift control means having control linkage whereby shiftingfrom high to low through a neutral position may occur in a straightline. This shift pattern is advantageous for many reasons including thefact that it requires a minimum of operator effort to accomplishshifting. Thus, the provision of a speed selector valve which willaccommodate a straight-shift pattern in order to control a high-low gearreduction unit is the first problem to be solved by this invention.

While the aforementioned speed selector valve or means is sufficient tocontrol the application of actuation means on the gear reduction unit,such control would be impractically harsh. In order to reduce theproblem of harsh application of the actuation means or clutches on thegear reduction unit, an additional modulating valve or means isprovided. Such modulating means or valve functions to modulate theapplication of the actuation means on the gear reduction unit in orderto insure smoothness of operation of the unit.

Furthermore, it is now the practice in industry to provide safetydevices which prevent a tractor from being started unless the controlmeans or system is in a neutral position in order to avoid damage aspreviously mentioned. However, previous systems such as that disclosedin US. Pat. No. 3,091,976, assigned to the assignee of this invention,have been concerned with a U-shaped shift pattern which requires returnof the control system linkage to neutral from only one direction. Theuse of a straight-shift control means as described above, on the otherhand, requires the return of the control linkage to a central, neutralposition from either of two directions. A problem thus posed is toprovide a safety override system which will function in this manner andreturn the control linkage to the neutral position from either of twopositions.

A solution to the above outlined problems is the subject of thisinvention. The solution takes the form of a control valve or meanscomprising a speed selector valve means, a pressure modulating reliefvalve means, and a safety valve means.

It is therefore an object of this invention to provide a control meansin the form of a control valve for selectively directing hydraulic fluidto a plurality of actuation means or clutches which, in turn control aplurality of speeds or power transfer modes of a gear reduction unit.

It is a further object of this invention to provide a control means fora hydraulically actuable gearreduction unit which has means formodulating the application of actuation means or clutches on the gearreduction unit.

It is a further object of this invention to provide a control means fora hydraulically actuable gear reduction unit having a safety overridemeans which will return the control means to a neutral position inresponse to low hydraulic pressure.

It is a still further object of this invention to provide a controlmeans for a hydraulically actuable gear reduction unit having a safetyoverride means which will return the control means to a neutral positionin response to low hydraulic pres sure while being insensitive to shortpressure transients caused by shifting.

It is a still further object of this invention to provide a controlmeans for a hydraulically actuable gear reduction unit having a safetyoverride means which will return the control means to a neutral positionfrom either of two directions in response to low hydraulic pressure.

BRIEF DESCRIPTION OF THE DRAWING The FIGURE discloses a cross-sectionalview of the hydraulic control valve of this invention in associationwith a system including a hydraulic gear reduction unit which iscontrolled by the control valve.

DETAILED DESCRIPTION Referring to the FIGURE. there is shown thearrangement of a control system including a control valve showngenerally at 10 which is mechanically linked to a manual control levershown generally at l2 and which controls a high-low power shift gearreduction unit shown generally at 14.

The gear reduction unit has an input member or shaft 16 which may bealternatively connected to an output member or shaft 18 through ahigh-range clutch or actuation means shown generally at 20 or forreduced speed'through a lowrange clutch or actuation means showngenerally at 22. The low-range actuation means includes a sun gear 24, astepped reducing gear 26, and a sun gear 28. The stepped reducing gearmay be mounted for rotation by suitable bearing means (not shown) on astationary shaft 30.

The system is powered by means of a source of fluid pressure comprisinga pump 32 by means of lines 34, 36 through filter 38. The system isillustrated with the parts in the positions which they assume when thefluid power source or pump is in operation and the controls are in theneutral position. Located within a common housing 40 are a plurality ofvalves consisting of a safety valve or means 42, a pressure modulatingrelief valve or means 44, and a speed selector valve or means 46.

The safety valve includes a safety spool 48 which is mechanically linkedto a speed spool 50 of the speed selector valve by means of a pivotlever 52 which has an end linked to each spool and is pivotally mountedon pivot mount 54 in order to provide coordinated axial movement of bothspools. A shift lever 56 is mechanically linked to the pivot lever endof the speed spool. Speed spool 50 includes a high-range detent annulus58, a neutral detent annulus 60, and a low range detent annulus 62.Speed spool 50 is maintained in the high, low, or neutral position bymeans of a spring-biased ball or detent means 64.

Operation of pump 32 introduces fluid under pressure into chamber 66 bymeans of lines 34, 36 through filter 38 as previously mentioned. Thehydraulic fluid at a pressure of approximately 250 p.s.i. in chamber 66is communicated to either high-speed clutch or low-speed clutch 22 uponmanual actuation of speed spool 50 by means of shift lever 56.

For example, when the operator selects a high speed driving mode heplaces lever 56 into position 56. This causes speed spool 50 to be movedleftwardly, thus communicating the working fluid in chamber 66 withhigh-speed clutch 20 by means of line 68.

Conversely, if shift lever 56 is moved in the opposite direction, theworking fluid in chamber 66 is communicated with low-speed clutch 22 bymeans of line 70. A plurality of axially oriented slots 74, 76 aremachined on both edges of speed spool lands 78, 80, respectively. Theseslots permit gradual activation of the clutches by allowing finercontrol of the working fluid to the clutches when the spool lands arereciprocated in mating axial bores 79, 81. In this manner the operatormay inch the vehicle by small, incremental movements of shift lever 56.

As cylinder 82 in high-speed clutch 20 is filled, pressure in chamber 66drops to approximately 30 psi. before it begins to rise again. At thebeginning of the pressure rise, speed check valve 84 having orifice 86extending therethrough is at its rightmost position in speed check valvechamber 88. In this position the speed check valve abuts against housingstop 90 having stop slot 92 therein.

As pressure in chamber 66 begins to rise, fluid meters through passage94 and chamber 88 and thence through orifice 86 and stop slot 92 intochamber 96. This causes load piston 98 to move from approximatelyposition 98 leftwardly to the position shown in the FIGURE where itabuts the housing. It should be further noted that the rightward limitof travel of load piston 98 is defined by the point at which it abutsthe adjacent housing.

It should be parenthetically noted that load piston 98 assumed itsposition 98 due to a pressure drop in chamber 66 communicated to chamber96 by the aforementioned passages which was caused by a previous speedshift. During the previous shift, the resultant pressure drop in chamber66 quickly reduced pressure in chamber 96 by means of the aforementionedpassages which permitted spring 100 to force load piston 98 into chamber96 to position 98 and thereby to compress fluid in chamber 96 which, inturn, forced check valve 84 to move leftwardly in chamber 88 and therebyallow dumping of fluid from chamber 96 into an annulus 102 and thenceinto speed spool bore 104 and finally through a drain 106.

At any point above fill, the action of load piston 98 exerts a leftwardforce on modulating relief valve spool 108 by means of spring 100.Conversely, spool 108 exerts a rightward force on load piston 98 bymeans of the same spring.

Rising pressure in chamber 66 is also communicated to slug cavity 110 inone end of spool 108 by means of cross passage 112 and axial passage114. The pressure fluid thus communicated urges spool 108 rightwardly aspressure in slug cavity 110 causes generally cylindrically shaped slug116 to move leftwardly relative to the cavity while abutting against thevalve housing. Pressure forces in chamber 96 distributed over therelatively large rightward end of load piston 98 are transmitted bymeans of spring 100 to modulating relief valve spool 108 to overcome thepressure forces on the smaller pressure area of slug 116 in cavity 110.The metering of fluid from chamber 66 to a drain (not shown) by meansofa drain annulus 118 is decreased due to the leftward movement of spoolland edge 120 toward land 122, whereupon pressure in chamber 66 rises toa pressure approaching the approximately 250 p.s.i. value which isrequired to lockup the clutches.

Clutch modulation is provided by the delay of pressure rise in chamber66 from the time it takes to fill a given clutch completely through thetime that it takes to fill chamber 96 and until spool 108 reduces fluidto drain through annulus 118 and thus stabilizes. Sufficient drainpassages or chambers are provided to eliminate unwanted pressureinfluences on slug 116, spool 108, and load piston 98. For example, slugdrain chamber 124 leads to a drain (not shown). Similarly, drain 126facilitates draining of the spring ends of spool 108 and load piston 98by means of passage 128 and annulus 130. Drain 126 also serves to drainthe spring ends of safety spool 48, the operation of which will behereinafter described.

The operation of safety valve 42 is as follows. Fluid from chamber 66communicates through a passage 129 in the housing through a line 130 anda check valve 132 through line 134 into chamber 136. Fluid pressure inchamber 136 acts equally on identical safety piston 138, 140 which areaxially movable in axial bores 142, 144 respectively. The leftmostpiston 138 slidably encompasses the leftmost end of safety spool 48 bymeans of axial bore 145 while the rightmost piston 140 similarlyslidably encompasses the rightmost end of spool 48 by means of axialbore 147. Two biasing compression springs or means 146, 148 are locatedin stepped portions of pistons 138, 140 respectively. These biasingcompression springs which act between the housing and their respectivepistons, possess spring constants such that when operating pressures aremaintained in the system the pistons will take the position shown in theFIGURE wherein the spring ends abut the housing. However, when operatingpressure drops for a period (2 seconds) in excess of the normal shifttransient (0.6 second), the compression springs will force theirrespective pistons toward each other until they come to rest on the leftand right land edges of central, annular land 150, and left and rightedges of projecting land 152 on generally rodlike safety spool 48. In sodoing, safety spool 48 will be centered, which movement will betransmitted through pivot lever 52 to center the neutral detent annulus60 of speed spool 50 over detent means 64. Thus, the control valve willbe automatically repositioned to a neutral position upon occurrence ofalow operating pressure.

Check valve or means 132 is provided with a one-way check 154 having anorifice 156 therethrough and biased by a spring 158. The one-way checkallows free passage of fluid from chamber 66 to safety valve chamber 136and is calibrated to meter safety valve chamber fluid back to chamber 66over a period of two seconds. The delay is sufficient to permit thenormal shift cycle to occur without signaling the safety valve tocommence its centering function. Safety valve spring chambers 160, and162 are connected to drain 126 by means of passages to eliminateunwanted pressure influences as previously mentioned.

The sequence of events that takes place from one shift to another is asfollows. Initially, the transmission control is positioned with lever 56in neutral. When the vehicle engine is started, initiating flow frompump 32, the filling pressure in chamber 66 causes immediate rightwardmovement of check valve 84. Pressure in chamber 66 is also communicatedto safety valve means 42 via conduit 130, check valve 132, and conduit134 to chamber 136. Check valve 132 is provided with a poppet having anorifice which allows fast flow in the rightward direction. Thepressurization of chamber 136 is such as to move safety piston 138leftwardly and safety piston 140 rightwardly to their full limit oftravel, thereby compressing springs 146 and 148, respectively.

As chambers 66 and 136 and associated passages are filled, a point isreached where the initial pressure setting of pressure-modulating reliefvalve means 44 is overcome. Until such a pressure is reached, spool 108is disposed fully to the left against slug 116 such that spool land edge120 blocks off communication between chamber 66 and drain 118. Pressurein chamber 66 is also communicated to chamber 96 and load piston 98through orifice 86 in check valve 84. When the pressure in chamber 66exceeds the initial pressure setting, spool 108 moves rightwardly torelieve and meter fluid to drain 118.

Thus, the pressure in chamber 66 acts through passages 112 and 114against a slug 116 to urge the spool to the right. At the same time,pressure in chamber 96, distributed over the full cross-sectional areaof load piston 98, urges spool 108 to the drop in the pressure inchamber 66 because passage 68 and cylinder 82 must be filled to engageactuation means 20. This drop in pressure in chamber 66 causes a checkvalve 84 to move rapidly to the left, communicating chamber 96 to drain106. Reducing the pressure in chamber 96 causes rapid rightward movementof load piston 98 to reset the modulating relief valve 44. The pressurein chamber 66 then drops to some low fill pressure value. At this lowpressure value, modulating relief spool 108 moves to the left to blockoff communication of chamber 66 to drain 118.

During filling of cylinder 82, check valve 84 moves rightwardly againand the pressure in chamber 66 increases to the initial setting of themodulating relief valve. At this initial setting, the pressure actingagainst slub 116 causes rightward movement of spool 108 off its seat sothat pressure in chamber 66 is relieved to drain 118. Load piston 98begins its leftward movement from a rightward position such as 98' andproceeds to its fully leftward position, during which interval a gradualrate of pressure rise in chamber 66 and its actuating means occurs topermit a smooth engagement of the clutches of the transmission.

During the period of filling of the clutch when chamber 66 is at afairly low pressure, the higher pressure in chamber 136 drops slightlyas some fluid travels from passage 134, through orifice 156, and intopassage 130 as the pressures attempt to equalize. However, the durationof the low-pressure, clutchfilling period and initial portion of thepressure rise period is so short that orifice 156 does not permit enoughfluid flow from chamber 136 to cause safety pistons 138 or 140 to abutland 152. Only when the delay in achieving a normal pressure in chamber66 passes beyond the normal transient period does the flow quantitythrough orifice 1S6 allow the pistons to center the safety valve means42 through springs 146 and 148.

It is understood that the foregoing description is merely illustrativeof a preferred embodiment of the invention and that the scope of theinvention is not to be limited thereto, but is to be determined by thescope of the appended claims.

What is claimed is:

1. in a transmission control system, a control valve comprising ahousing, a position selector valve means within said housing foractuating a transmission, said position selector valve means having afirst and a second position on opposite sides of a central, neutralposition, said position selector valve means serving to direct pressurefluid from a source of fluid pressure to a transmission for actuation ofcorresponding first or second positions of said transmission, means forreturning said position selector valve means to said central, neutralposition when fluid pressure in said position selector valve means dropsbelow a predetermined value for a predetermined time such as whenmalfunction or normal shutdown of the fluid power source occurs, therebypreventing system damage and wherein the means for returning theposition selector valve means to the central, neutral position comprisessafety valve means within said housing means operatively connecting saidsafety valve means to said position selector valve means, and meanscommunicating said safety valve means with fluid pressure wherebymovement of said safety valve means in response to low fluid pressureresults in coordinate movement of said position selector valve means.

2. The invention of claim 1 further including a means which fluidlycommunicates the safety valve means with the position selector valvemeans and which operates to allow a normal shift cycle to occur withoutsignaling the safety valve means to commence its cepterin function.

3. The invention 0 claim 2 further including a pressure modulatingrelief valve means within said housing which operates to modulate theoperation of said position selector valve means.

4. The invention of claim 2 wherein the means which fluidly communicatesthe safety valve means comprises a one-way check having an orificetherethrough and a spring biasing said check.

5. The invention of claim 2 wherein the safety valve means furthercomprises a generally rodlike safety spool having a projecting landthereon, said safety spool being contained in said housing and beingaxially movably retained therein by identical safety pistons havingaxial bores encompassing opposite ends of said safety spool, saidpistons being axially movable in separate axial bores in said housing,which bores are separated by a central, annular land, said pistons beingbiased toward each other by spring means contained within said housingbores, and said means operatively connecting said safety valve meanscomprises a pivot lever pivotaily mounted intermediate its ends on apivot mount and having one end operatively connected to one end of saidsafety spool and the other end operatively connected to said positionselector valve means.

6. The invention of claim 5 wherein the spring means comprise springshaving spring constants such that when operating pressures aremaintained in the position selector valve means the fluid pressurecommunicated to the safety valve means will cause the pistons tocompress the springs and allow free move ment of the safety spool andwhen fluid pressure drops below a minimum value the springs will forcethe pistons against the center land and projecting land on the safetyspool from opposite sides such that the safety spool will be centeredand thereby center the position selector spool in the neutral positionby means of the pivot lever.

7. The invention of claim 6 wherein the position selector valve meanscomprises a position spool having a pair of position spool landsthereon, said lands being axially movable within mating axial bores andwherein one end of said position spool is adapted for operativeattachment with a shift lever.

8. The invention of claim 7 further including first, neutral and secondposition detent annuli on said position spool, and a detent meansmounted to cooperate with said annuli in order to maintain a particularposition.

9. The invention of claim 7 wherein said position spool lands defineedges and wherein a plurality of axially oriented slots are extant onthe edges thus defined thereby permitting finer control of the workingfluid.

1. In a transmission control system, a control valve comprising ahousing, a position selector valve means within said housing foractuating a transmission, said position selector valve means having afirst and a second position on opposite sides of a central, neutralposition, said position selector valve means serving to direct pressurefluid from a source of fluid pressure to a transmission for actuation ofcorresponding first or second positions of said transmission, means forreturning said position selector valve means to said central, neutralposition when fluid pressure in said position selector valve means dropsbelow a predetermined value for a predetermined time such as whenmalfunction or normal shutdown of the fluid power source occurs, therebypreventing system damage and wherein the means for returning theposition selector valve means to the central, neutral position comprisessafety valve means within said housing, means operatively connectingsaid safety valve means to said position selector valve means, and meanscommunicating said safety valve means with fluid pressure wherebymovement of said safety valve means in response to low fluid pressureresults in coordinate movement of said position selector valve means. 2.The invention of claim 1 further including a means which fluidlycommunicates the safety valve means with the position selector valvemeans and which operates to allow a normal shift cycle to occur withoutsignaling the safety valve means to commence its centering function. 3.The invention of claim 2 further including a pressure modulating reliefvalve means within said housing which operates to modulate the operationof said position selector valve means.
 4. The invention of claim 2wherein the means which fluidly communicates the safety valve meanscomprises a one-way check having an orifice therethrough and a springbiasing said check.
 5. The invention of claim 2 wherein the safety valvemeans further comprises a generally rodlike safety spool having aprojecting land thereon, said safety spool being contained in saidhousing and being axially movably retained therein by identical safetypistons having axial bores encompassing opposite ends of said safetyspool, said pistons being axially movable in separate axial bores insaid housing, which bores are separated by a central, annular land, saidpistons being biased toward each other by spring means contained withinsaid housing bores, and said means operatively connecting said safetyvalve means comprises a pivot lever pivotally mounted intermediate itsends on a pivot mount and having one end operatively connected to oneend of said safety spool and the other end operatively connected to saidposition selector valve means.
 6. The invention of claim 5 wherein thespring means comprise springs having spring constants such that whenoperating pressures are maintained in the position selector valve meansthe fluid pressure communicated to the safety valve means will cause thepistons to compress the springs and allow free movement of the safetyspool and when fluid pressure drops below a minimum value the springswill force the pistons against the center land and projecting land onthe safety spool from opposite sides such that the safety spool will becentered and thereby center the position selector spool in the neutralposition by means of the pivot lever.
 7. The invention of claim 6wherein the position selector valve means comprises a position spoolhaving a pair of position spool lands thereon, said lands being axiallymovable within mating axial bores and wherein one end of said positionspool is adapted for operative attachment with a shift lever.
 8. Theinvention of claim 7 further including first, neutral and secondposition detent annuli on said position spool, and a detent meansmounted to cooperate with said annuli in order to maintain a particularposition.
 9. The invention of claim 7 wherein said position spool landsdefine edges and wherein a plurality of axially oriented slots areextant on the edges thus defined thereby permitting finer control of theworking fluid.